The present invention relates to a battery discharge indicator. More particularly, the present invention relates to a battery discharge indicator which indicates the voltage of the battery and automatically disconnects a load connected to the battery when the battery voltage drops below a predetermined value. Furthermore, the present invention relates to battery discharge indicators having a self-test capability and tamper-proof features.
Various devices for sensing the state of charge of a battery and for disconnecting a load connected to the battery are known in the prior art. A battery connected to a load will drive the load until the battery is incapable of supplying the current necessary for proper operation of the load. For example, a truck battery connected to a lift pump will drive the pump until the continued loading of the battery causes the battery charge to be depleted so that the battery can no longer supply the required voltage for operating the pump.
Although devices are known for sensing the state of charge of a battery and for disconnecting a load connected to the battery when the charge drops below a predetermined discharge level, these devices do not disconnect the load until the charge on the battery drops below the predetermined discharge level for a specified period of time. Many of the foregoing devices provide no visual indication of the state of charge of the battery so that the load continues to drain the battery of its charge until the load is automatically after the specified interval of time has expired. Accordingly, an operator is not given the opportunity to disconnect the load from the battery and to re-charge the battery before it becomes substantially depleted of its charge.
Additionally, continued operation below the predetermined discharge level for the specified interval of time before disconnection of the load results in further draining of the battery and, unless the discharge level is chosen to be sufficiently modest, the battery may become damaged by the time disconnection takes place.
Furthermore, conventional devices for indicating the state of charge of a battery do not have a self-test capability. That is, these devices operate only in response to the actual rate of decay of the battery charge. Consequently, a conventional device may be defective, as manufactured, or may malfunction during the course of operation, and be unable to disconnect the load from the battery when the predetermined discharge level is reached. As a result, the battery may become damaged permanently due to the continued operation below the discharge level.
For these reasons, a battery discharge indicator device is needed for automatically indicating the state of charge of the battery and for providing the operator with an opportunity to disconnect the battery from the load so that it can be removed and recharged. During automatic operation, such a device should be capable of disconnecting the load when, due to component failure, the defice is unable to provide an indication that the battery voltage has dropped below the predetermined discharge level. Further, during automatic operation, the device should be relatively immune to sudden disconnection and reconnection of the battery. The device should also have a self-test capability to forewarn the operator that the device will not operate to indicate the state of charge of the battery or disconnect the load when the battery charge is sufficiently depleted.
Moreover, it is desirable that the self-test capability operate under a variety of fortuitous conditions. For example, it is desirable that the self-test capability remain operative despite the level of discharge of the battery; regardless of the presence of a load at the output terminals of the battery; and despite operator error in prolonging the self-test operation of the device. In addition, the self-test feature of the device should be operable at any time during the automatic operation of the device without interrupting that operation.
A principal advantage of the present invention is that it automatically indicates the state of charge of a battery with respect to two voltage levels, thereby permitting the operator to remove the battery and re-charge it before the load is automatically disconnected.
Another advantage of the present invention is that the battery can be safely operated under load, although the opportunity for removing and re-charging the battery has passed, and then automatically disconnected from the load as soon as the battery voltage reaches the predetermined discharge level.
Yet another advantage of the present invention is that it can automatically disconnect a load connected to the battery when, due to component failure, the indication that the battery voltage has dropped below the predetermined discharge level cannot be provided.
An additional advantage of the present invention is that it can operate automatically to indicate the state of charge of the battery despite sudden disconnection and reconnection of the battery.
A further advantage of the present invention is that the battery voltage need not remain below the predetermined discharge level for a preselected period of time before the load can be automatically disconnected.
A still further advantage of the present invention is that it can automatically test itself.
A still further advantage of the present invention is that it can automatically test itself despite the level of discharge of the battery; regardless of the presence of a load at the output terminals of the battery; and despite operator error in prolonging the self-test operation of the invention.
Other advantages appear below in the detailed disclosure of the invention.